Let's run down the list of improvements.
First off, the current design is just kind of bland. A stone brick box with chests and pillars.
Dungeons be changed to a larger, slightly cavernous room, lit with a hearth fire in the center. The best loot would spawn in four chests arranged around the fire, but this is where the Orcs and their chieftain would spawn.
Branching off of the main room would be several (two to four) small tunnels, each with a single chest. These branches can be empty except for the chest, may contain an Orc bed, or can be blocked off by Orc bars with a skull behind them.
A crafting table of the owning faction has an unlikely chance to spawn in one of the branches.
All Orc factions would get their own dungeon, because who doesn't like a little bit of variety? Most faction variations would have patches of their faction's brick on the walls of the main room, with the exception of the more organized ones. For example...
GundabadWould have patches of default stone brick (More uncommonly can spawn as Dwarven brick) along the walls. Waste blocks and skulls would spawn scattered around the dungeon, and there would be a chance for no fire to spawn in the center. Loot would be a mix of Orc equipment, bones, skulls, rotten flesh, but would also have more gems and treasure, like gold, silver, etc. Mithril would have a very, very slightly better chance to spawn.
Very ruined, with patches of stone brick mixing with what remains of Angmar brick, some of it Gulduril-ed. The hearth blocks in the center can have a chance to be unlit, but Gulduril torches can spawn along the walls. Loot would include low durability Angmar equipment, the usual treasure, and other miscellaneous drops.
Patches of Dol Guldur brick cover the walls, again with some of it in the Gulduril state. The hearth in the center would be slightly more sophisticated than the previously mentioned ones, surrounded by Dol Guldur brick, spiked at the corners. Webs would be common, with some of the branching tunnels blocked off with them. Spiders would spawn along with Orcs here, and loot would include Dol Guldur equipment, along with some loot taken from Dwarven and Elven prisoners.
These would look much less cavernous than the others. Rather than Uruk brick simply appearing in patches through the stone, it would line the walls, although the ceiling would still be domed with rock. Orc torches would line the tunnels, although hallways would be a better word, and the iron bar-variant of branch wouldn't spawn. Orc forges would spawn in the main room, and chest loot would include Uruk equipment, meat, and bones, but the only ores/ingots be Iron and Uruk steel.
MordorSimilar to the Isengard Dungeon, this is much less cave-like than the others. The hallways would only consist of the jail and normal chest variants, so no Orc beds can be found in these. Like the Dol Guldur Dungeon, the hearth is spiked, and cannot spawn unlit. Orc torches are found on pillars and the hallways are lit with blocks of Durnaur under Orc bars. Wherever tunnels do not spawn, an Orc forge spawns instead. Chest loot consists of all the normal items, but also Mordor equipment.
And that's the suggestion. I hope to get pictures to shorten down the currently very long and confusing descriptions of each variant, and please leave any comments or constructive criticism you have down in the comments.